Also enables debug symbols in release profile by default. Until
Alacritty ships, there's going to be lots of perf analysis which needs
debug symbols.
The PriorityMutex low priority method was never used. Now it's just a
fair mutex.
This is only like the third time I've made this change. The issue of
having a blank screen at startup is due to x11 event loop + glX
interactions. Not sure what the problem is specifically, but
glXMakecurrent was blocking until the x11 event loop advanced.
The input and rendering are able to live on the same thread while still
removing unnecessary renders due to the
glutin::WindowProxy::wakeup_event_loop() method. The PtyReader just
kicks the event loop when there's something to do; otherwise, the event
loop just waits for something to happen and _doesn't_ draw in free run
mode.
Joe Wilm